The invention relates to the field of construction equipment machines such as excavators, mini excavators, etc, and more particularly to such machines having an upper frame and a lower frame rotatably connected.
On FIG. 1 is depicted a conventional excavator 10. It comprises an upper frame carrying the excavator's superstructure 12 which comprises the driver's cabin 14 and an engine compartment 16. The upper frame carries the machine's main work equipment: a digging assembly 18. Typically, the digging assembly 18 can have boom 20 which is pivotably connected around a horizontal axis on the upper frame. The boom 20 can be lowered and lifted vertically by a boom cylinder 22. At the free end of the boom 20, an arm 24 may be pivotably connected around another horizontal axis, and it can be lowered and lifted by an arm cylinder 26. At the free end of the arm 24, a working tool, such as bucket 28, is pivotably connected around another horizontal axis and it can be pivoted relative to the arm 24 by a bucket cylinder 30.
The lower frame carries the undercarriage 32 of the machine 10, which comprises mainly the drivetrain 34 of the machine. In the example shown, the drive train is in the form of a pair of endless tracks but it could also be made of a set of wheels. In the example shown, the undercarriage 32 also comprises a working tool which is for example in the form of a front blade 36. For this blade to be perfectly convenient, it may desirable that it not only is capable of being lowered and lifted with respect to the undercarriage but also that it can be rotated around a horizontal axis and/or around a vertical axis. As it is well-known, the superstructure 12 of the machine can swivel around a vertical axis with respect to the undercarriage thanks to a suitable mechanical link between the upper frame and the lower frame, with the possibility of both frames rotating with respect to each other around a vertical axis. In many cases, the superstructure can swivel 360 degrees.
Most construction equipment machines use a hydraulic pressure system to operate the various working tools 28, 36 carried by the machine, as well as to operate the drive train 34. The hydraulic pressure system comprises usually a Diesel engine which drives at least one hydraulic pump which itself feeds pressurized fluid to various actuators through hydraulic circuits comprising hydraulic lines, distributors, valves, etc.
The major parts of the hydraulic pressure system are usually located on the upper frame of the machine. On the other hand, some of the tools carried by the machine may be located on the lower frame, such as the blade 36 mentioned above, not to mention the fact that the drivetrain, carried of course by the lower frame, usually comprises a hydraulic motor and possibly a hydraulic actuated gearbox.
Therefore, the machine is equipped with a rotary joint which provides hydraulic passages which permit the hydraulic lines to pass from the upper frame to the lower frame without being interrupted and without impeding the free swiveling of the two frames. Therefore, the rotary joint may have an upper part connected to the upper frame and a lower part connected to the lower frame. The upper and lower parts of the rotary joint have for example respective annular contact surfaces bearing one against the other, and at least one of the annular contact surfaces comprises an annular groove which is closed by either a corresponding annular groove on the other contact surface, or simply closed by that other contact surface. The groove(s) define an annular fluid flow path at the interface between the parts of the rotary joint. An upper portion of a hydraulic line (for example a hose or a pipe) is connected to the upper part of the rotary joint while a lower portion of the hydraulic line (made for example of another hose or pipe) is connected to the lower part of the rotary joint, both being fluidly connected to the annular groove. With this construction the upper and lower portions of the hydraulic line are fluidly connected one to the other irrespective of the angular position of the two parts of the rotary joint. Other types of rotary joints could be used in the context of the invention.
Of course, this means that the rotary joint needs to have one fluid flow path for each independent hydraulic line which is to be passed through the rotary joint. Therefore, one can easily understand that there is a strong motivation to keep the number of hydraulic lines to be passed through the rotary joint to a minimum.
Another constraint on construction equipment machines is at that they have to be able to work in a humid environment, up to the point where they should be capable of being fully operational even when the undercarriage is partly or totally submerged in water. One consequence is that it is most preferable not to have any electrical system running on the lower frame. Therefore it is well-known that any actuator located on the lower frame should not be piloted by an electrically piloted valve but rather by a hydraulically piloted valve. But then, given the fact that it is essential to keep the number of a hydraulic lines passing through the rotary joint to a minimum, this tends to limit the number of independently controlled devices which can be located on the lower frame.
It is desirable to provide a new conception of hydraulic circuitry which permits to have several independently controlled devices on the undercarriage, without necessitating the use of a very complex and expensive rotary joint. Moreover, it is desirable to make it possible to add new functionalities to an existing machine, as a retrofit, without having to change or modify the rotary joint.
According to an aspect of the invention, the invention provides for a construction equipment machine having a lower frame and an upper frame rotatably connected through a rotary joint, the machine having at least one hydraulic pilot circuit comprising a primary hydraulic pilot line running from the upper frame to the lower frame through said rotary joint for controlling, from the upper frame, the operation of at least one hydraulic device located on the lower frame, said hydraulic pilot circuit comprising: a pressure regulating system capable of setting in the pilot circuit a pilot pressure having a value, said pressure regulating system being located on the upper frame; a hydraulic pressure controlled selecting system which is located on the lower frame and is fed by said primary pilot line, at least two independent secondary pilot lines located downstream of said pressure controlled selecting system in said hydraulic pilot circuit, and wherein said hydraulic pressure controlled selecting system is capable of selectively and independently supply or not supply pressurized fluid to the at least two independent secondary pilot lines, responsive to said value of the pilot pressure.